On 21 June 1963 Schweitzer was appointed managing director and chairman of the executive board of the IMF, and he assumed his duties on 1 September 1963.

Schweitzer was appointed to a second five-year term as managing director and chairman of the board of the IMF on 15 May 1968.

Schweitzer's term as the IMF's managing director was a critical period, not only due to the collapse of the Par Value System, but also for the creation of the special drawing rights (SDR), as an international reserve asset (1968); the establishment of the two-tier gold market, and the work of the Committee of Twenty of the International Monetary System on reforming the international financial system.

Schweitzer was commissioned as a lieutenant in the French Army after the outbreak of World War II.

When France fell in 1940, he joined the French Resistance and was later captured and held at the Buchenwald concentration camp, on the outskirts of Weimar, Germany, until it was liberated in 1945.